"_Lolìgo_ also is found in our seas; the thin, transparent rib, called the _dorsal blade_, you may probably find on the shore, the flesh that covered the blade being cleared entirely from it. The colour is either white or brown. It is called _sea-sleeve_. "The bone of the cuttle-fish, _Sepia officinalis_, is so frequently thrown on shore by the waves, that few persons visiting the sea-coast can be ignorant of its form. You have a large collection there I see, Lucy; and you are doubtless aware that this calcareous bone affords the _pounce_ of the stationers, when finely pulverized: it also forms one ingredient of tooth-powder. "The ink of this marine animal is contained in a bag: the use of the fluid is to colour the water around, in order to conceal itself from hostile attack. The flesh of some of these animals is used for food, and is frequently seen in the market at Naples. In the British isles it is not put to any culinary purpose. The ink of _Sepia_ can be prepared for a pigment, or paint. "The fifth and last order of the twelfth class is _Heteropoda_, which contains only a few genera, one of which I shall notice. [Sidenote: CARINARIA.] "_Carinaria_, the glass-nautilus, is a rare and very precious genus, containing but three species. The first, _Carinaria ritrea_, has been found in the Southern Ocean. There is a model of the shell in the British Museum; that of Paris possesses the shell itself. "_C. Mediterranea_ is found in the neighbourhood of Nice, and is frequent in the summer months. So thin and delicate is the shell that it is seldom found entire. "The shell of _Carinaria_ is wholly external, and is attached to the upper part of the body, apparently to protect the organs of respiration. The body is transparent, dotted with elevated points; on the lower part is a beautiful reticulated fin, of a reddish colour; with the end of this fin it floats along, carrying its delicate shell. The habit of the animal, which swims upon its back, reverses the natural position of the shell, which is on the upper part of the body when at rest." "That is one of the most remarkable creatures you have yet mentioned," said Charles; "I may chance to meet with a specimen when I travel." "Probably," replied Mr. Elliot; "but our lessons are now concluded--_Carinaria_ is the last genus." "How greatly we are obliged to you, father!" said Lucy: "but I hope you will still give us a little advice and assistance: we shall often be unable to determine the genera of some shells, I am sure, especially among the bivalves." [Sidenote: METHOD OF CLEANSING SHELLS.] "Most willingly: but tell me if you know the easiest method of cleaning shells when they become soiled, or when you purchase them in the natural state?" "That is a question I wished to ask."